Thin film field effect transistors (TFT), useful in flat panel display applications, at the current state of the art, involve a semiconductor layer with a channel defined by separated source and drain electrodes on one side and an insulated gate electrode on the other side that is centered with respect to the channel. The structure of the TFT device is usually fabricated through a set of serial deposition operations of carefully controlled layers on a substrate. The desired TFT electrical performance involves low voltage operation with high carrier mobility in the channel, and with current vs voltage output characteristics that include a steep slope followed by a saturation region.
The current TFT devices typically use amorphous silicon (a--Si:H) as the semiconductor and silicon oxide and/or silicon nitride as the gate insulator. Some attention in the art is being directed toward the use of semiconducting organic compounds as potential replacements for amorphous silicon as the semiconductor.
As the art is progressing, in addition to the ever increasing stringency of requirements for increases in density and responsiveness of the components, it is also becoming desirable that transparent substrates have mechanical flexibility, impact resistance and light weight. Meeting all the constraints is becoming more difficult to achieve. Many materials and processing techniques used in the fabrication of active matrix liquid crystal displays (AMLCD), that are based on a--Si: H TFT devices involve temperatures above 350 degrees C. which operates to eliminate many otherwise useful substrate materials. A need is growing in the art for a broader range of materials and processes for TFT devices, particularly under the rigorous criteria in the display type of application. Transparent plastic substrates for AMLCD are very desirable but cannot withstand temperatures above 150-200 degrees C.